In the past various parts, such as frame members, stile members, jamb members, etc. of a window have been made of metal with a vinyl or plastic layer or veneer of material applied to cover the metal for various purposes, such as aestetics and thermal insulation. Several disadvantages to such an approach include the ease with which the plastic or vinyl layer may be damaged and the relatively small amount of thermal insulation characteristics achieved thereby.
The present invention is described in detail herein with respect to a sliding window. However, it will be appreciated that the invention may be employed in other types of windows, such as double hung windows, windows with fixed glass or lights, and other types of windows. Moreover, the preferred material employed in the present invention is described herein as a vinyl material; alternatively, material may be identified equivalently as plastic material; in any event, the invention is intended to cover all vinyl, plastic and other materials that are non-metal and, thus, are relatively thermally nonconductive compared to the relatively high thermal conduction of metal. In the following description, reference is also made to aluminmum as the preferred metal portion of the window; it will be appreciated that other types of metal materials may be employed consistent with the invention. Still further, various portions of the window assembly of the invention are described below as being extrusions, i.e., a part being formed by extruding of material; however, it will be appreciated that the various parts of the invention may be formed or manufactured using techniques other than extusion.
Metal windows have various advantages over wood windows; for example, metal windows do not warp and can be made of materials that are extremely durable, weather resistant, etc. However, there are a number of disadvantages to metal windows, for example, the relatively high thermal conductivity thereof and, thus, the poor insulation characteristics, sweating or condensation of moisture on the metal, and the difficulty of providing aestetically pleasing appearance especially on the inside, i.e., the portion exposed in a room of a building.
The prior art includes sliding windows with sashes which slide between opened and closed positions in parallel tracks. Generally, such windows include two sashes which slide in parallel, offset tracks. Weather-stripping seals the spaces between the sashes and between the sashes and tracks. Although traditional window assemblies (including sashes and tracks) have been made of wood, modern manufacturing techniques and materials have made it possible to manufacture these components from metal or plastics, or a combination, and such combined materials have thermal, aesthetic and economic advantages. Usually the prior combination of metal and plastic windows have simply included a veneer of plastic glued or similarly bonded or adhered to the metal at an interface surface.